Described is an inflatable, expandable implant suitable for implantation in a human body. In general, it is a device that may be implanted in the body at a placement site in a lower profile form and expanded after placement. The implant may be used, for instance, to occlude or to support some region of the body.
The described implant may have a bladder with a substantially non-elastic bladder wall that defines a volume, and at least one bladder wall opening for introduction of filler material. In some examples of the implant, the bladder will have no passageway exterior to the bladder wall for passage of a body fluid from an end of the bladder to the other end. The bladder may have at least one closure for each of the at least one bladder wall openings. The closures operate to maintain the filler material within the bladder after its introduction. If the filler material is selected to be of the type that reacts in the bladder to form a non-flowing mass, a closure may not be necessary.
The use of occluding materials or implants over the past few years to occlude various areas in the body has expanded. For instance, in treating many vascular problems, the artificial blocking of blood flow, known generically as “embolization,” is used. The embolization of a blood vessel in an organ may be used to treat a variety of maladies; typically, though, embolization is used: 1) to control the bleeding caused by trauma, 2) to prevent profuse blood loss during an operation requiring dissection of blood vessels, 3) to obliterate a portion of or a whole organ having a tumor, or 4) to block the blood flow into abnormal blood vessel structures such as arterio-venous malformations (AVM's) and aneurysms. For such treatments, a variety of mechanical and chemical occludants are available. Such occluding materials include platinum and stainless steel microcoils. Platinum microcoils sold as Guglielmi Detachable Coils (GDC) by Boston Scientific Corporation are effective in many instances. However, significant skill is required to choose a coil size proper for the malady prior to delivery. Many anatomical sites are not suitable for use of microcoils, and removal is difficult.
Other occludants include polyvinyl alcohol sponges (Ivalone) and cyanoacrylate glues (n-butyl and iso-butyl cyanoacrylates). Of these, the cyanoacrylate glues have an advantage over other embolic materials in ease of delivery in that they are the only liquid embolics currently available to physicians. However, the constituent cyanoacrylate polymers have the disadvantage of being biodegradable. The degradation product, formaldehyde, is highly toxic to the neighboring tissues. See Vinters et al, “The Histotoxocity of Cyanoacrylate: a Selective Review”, Neuroradiology 1985; 27:279-291. Another disadvantage of cyanoacrylate materials is that the polymer will adhere both to the blood vessel and to the tip of the catheter. Thus physicians must retract the catheter immediately after injection of the cyanoacrylate embolic material or risk adhesion of the cyanoacrylate and the catheter to the vessel. Removal and choice of occludant size are major problems.
Another class of liquid embolic materials, precipitative materials, was invented in late 1980's. See Sugawara et al, “Experimental investigations concerning a new liquid embolization method: Combined administration of ethanol-estrogen and polyvinyl acetate”, Neuro Med Chir (Tokyo) 1993; 33:71-76; Taki et al, “A new liquid material for embolization of arterio-venous malformations”, AJNR 1990:11:163-168; Mandai et al, “Direct Thrombosis of aneurysms with cellulose acetate polymer. Part I: Results of thrombosis in experimental aneurysms.” J. Neurosurgery 1992; 77:497-500. These materials employ a different mechanism in forming synthetic emboli than do the cyanoacrylate glues. Cyanoacrylate glues are monomeric and rapidly polymerize upon contact with blood. Precipitative materials, on the other hand, are pre-polymerized chains that precipitate into an aggregate upon contact with blood.
In the precipitation method, the polymer is dissolved in a solvent that is miscible with blood, and upon contact with that blood, the solvent is diluted and the water-insoluble polymer precipitates. Ideally, the precipitate forms a solid mass and thus occludes the vessel.
The first such precipitative material used in this way was polyvinyl acetate (PVAc). Also, poly(ethylene-co-vinyl alcohol) (EVAL) and cellulose acetate (CA) dissolved in 100% dimethyl sulfoxide (DMSO) have also been used in clinical procedures. See Taki et al, “A new liquid material for embolization of arterovenous malformations”, AJNR 1990; 11:163-168 and Mandai et al, “Direct thrombosis of aneurysms with cellulose polymer: Part I: Results of thrombosis in experimental aneurysms”, J. Neurosurgery 1992; 77:497-500. Partially hydrolyzed polyvinyl acetate in, e.g., ethanol, is also an available member of this class.
Each of these precipitative materials shares potential use problems in that: (1) they introduce organic solvents into the body, materials that can damage microcapillary vessels and surrounding tissues and are also known to cause vasospasm of blood vessels, and (2) placement of a precipitating polymer and estimation of the resulting precipitated mass is, at best, an inexact science.
The filled bladder implant described herein does not share any of these problems when used as an occluding device, may placed with better precision, and (when designed to do so) may be removed from the implantation site.